Synthetic leather

ABSTRACT

Provided is a synthetic leather including: a base fabric that has a limiting oxygen index of 25 or more, and that is a knitted body of a yarn including a flame-retardant fiber having a limiting oxygen index of 25 or more, a cellulose-based fiber, and a carbon fiber; an adhesion layer containing a flame retardant, the adhesion layer being provided at at least one side of the base fabric; and a skin layer provided at a side of the adhesion layer opposite from a side at which the base fabric is provided.

TECHNICAL FIELD

The present invention relates to a synthetic leather.

BACKGROUND ART

In recent years, in place of natural leathers or fibrous sheets, synthetic leathers having excellent durability are widely used for automotive interior parts (such as instrument panels, door trims, seats, ceilings, or the like), rail vehicles, aircraft interior parts (such as trims, seats, ceilings, or the like), furniture, footwear such as shoes, bags, interior and exterior members for construction, clothing coverings, clothing linings, wall covering materials, and the like. For example, synthetic leathers used for aircraft interior parts and automobile interior parts need to be lightweight, durable, and have favorable fire resistance. There is a need for synthetic leathers which have a certain thickness and moderate elasticity in addition to the basic properties described above and which has a feel close to that of a natural leather.

From the viewpoint of favorable dimensional stability and processability, in general, synthetic leathers include a flexible resin layer for adjusting elasticity appropriately, and a skin layer having a leather-like appearance and excellent in abrasion resistance, at a surface of a fibrous sheet such as a base fabric.

With regard to highly airtight aircraft, vehicles, automobiles, or the like, favorable fire resistance is desired for synthetic leathers used for interior products. With regard to fire resistance of the synthetic leathers, it is considered to be important that a synthetic leather is hard to burn even if it comes in contact with flames, that, even if a part of a synthetic leather burns when it comes in contact with flames, the burning does not spread easily, and that a synthetic leather is hard to generate smoke when it burns, or the like.

In highly airtight aircrafts, vehicles, automobiles, or the like, if a generation of smoke due to fire is considerable, the view is more likely to be blocked, and the smoke is more likely to be inhaled. Therefore, for a synthetic leather used for aircraft interior parts, vehicle interior parts, automobile interior parts, or the like, in particular, suppression of smoke generation when in contact with flames is desired, in addition to flame retardancy, as fire resistance. Suppression of smoke generation and a low smoke concentration when a synthetic leather is exposed to flames are important criteria from the viewpoint of securing visibility in a highly airtight space.

In order to improve flame retardancy, a synthetic leather obtained by impregnating a base fabric with a nitrogen-based or phosphoric acid-based flame retardant has been proposed (see Japanese Patent Application Laid-Open (JP-A) No. 2006-77349).

Furthermore, the applicant of the present application has previously proposed a synthetic leather including a water-based polyurethane adhesion layer and a water-based polyurethane skin layer in this order on a synthetic leather base fabric, which is a knitted body having an interlock knitted structure using a yarn including a flame-retardant fiber having a limiting oxygen index (LOI value) of 25 or more and a cellulose-based fiber, the knitted body having a mass of from 150 g/m² to 250 g/m², an LOI value of the knitted body being 25 or more (see Japanese Patent Application Laid-Open No. 2013-072141).

SUMMARY OF INVENTION Technical Problem

However, the synthetic leather described in JP-A No. 2006-77349 has a problem that the finished quality is inferior when the thickness or strength of a woven fabric or a non-woven fabric used for the base fabric is not sufficient, in a case in which, for example, the leather is used for a seat or the like. Furthermore, since at the time of production, a base fabric is impregnated with a flame retardant or the like, and then dried and adhered to a resin layer, the production process is complicated, and there is a problem that a flame retardant may cause toxic gas or smoke generated during burning depending on the types of the flame retardant used.

Although a synthetic leather described in JP-A No. 2013-072141 has a feel close to that of a natural leather, favorable durability, processability and flame retardancy, and has a function of suppressed generation of toxic gas even when burned, there is still room for improvement in terms of suppression of smoke generation during burning.

An object of an embodiment of the invention is to provide a synthetic leather which is excellent in flame retardancy and which has a suppressed ability to generate smoke during burning.

Solution to Problem

Means for solving the above-described problems include the following embodiments.

-   [1] A synthetic leather including: a base fabric that has a limiting     oxygen index of 25 or more, and that is a knitted body of a yarn     including a flame-retardant fiber having a limiting oxygen index     (hereinafter, sometimes referred to as LOI value) of 25 or more, a     cellulose-based fiber, and a carbon fiber; an adhesion layer     containing a flame retardant, the adhesion layer being provided at     at least one side of the base fabric; and a skin layer provided at a     side of the adhesion layer opposite from a side at which the base     fabric is provided.

[2] The synthetic leather according to [1], wherein the flame-retardant fiber includes one or more selected from the group consisting of an aramid fiber, a meta-aramid fiber, a polyphenylene sulfide fiber, an acrylic fiber, a vinyl chloride fiber, a polyclar fiber, a vinylidene chloride fiber, an acrylic-vinyl chloride copolymer fiber, and an acrylic-vinylidene chloride copolymer fiber.

[3] The synthetic leather according to [1] or [2], wherein the carbon fiber includes one or more selected from the group consisting of a polyacrylonitrile (PAN)-based fiber, a pitch-based fiber, and a phenolic fiber.

-   [4] The synthetic leather according to any one of [1] to [3],     wherein a content of the carbon fiber is from 20% by mass to 40% by     mass with respect to the total mass of the yarn constituting the     knitted body, a content of the cellulose-based fiber is from 25% by     mass to 45% by mass with respect to the total mass of the yarn     constituting the knitted body, and a total content of the     flame-retardant fiber and the carbon fiber is greater than the     content of the cellulose-based fiber. -   [5] The synthetic leather according to any one of [1] to [4],     further including an intermediate layer between the adhesion layer     and the skin layer. -   [6] The synthetic leather according to [5], wherein the intermediate     layer contains a flame retardant.

Advantageous Effects of Invention

According to one embodiment of the present invention, a synthetic leather having favorable flame retardancy and which has a suppressed ability to generate smoke during burning.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic sectional view showing an embodiment of a synthetic leather in the disclosure.

FIG. 2 is a schematic sectional view showing another embodiment of the synthetic leather in the disclosure.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the synthetic leather according to the disclosure will be described in detail by way of specific examples of embodiments, but the invention is not limited thereto in any way, and can be implemented with appropriate modifications within the scope of the object of the invention.

Herein, numerical ranges indicated using “to” mean a range including the numerical values described before and after “to” as the minimum value and the maximum value, respectively.

Herein, the amount of each component in a composition means, if a plurality of substances corresponding to each component are present in the composition, the total amount of the plurality of substances present in the composition.

Herein, the term “process” includes not only a process independent from other processes but also a process which cannot be clearly distinguished from other processes as long as a desired purpose of the process can be achieved.

In each of the drawings, components having the same reference numerals indicate that they are the same components.

With regard to the stepwise numerical ranges described herein, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of another stepwise numerical range. In the numerical ranges described herein, upper limit values or lower limit values of the numerical value ranges may be replaced with values described in Examples.

<Synthetic Leather>

The synthetic leather according to the disclosure includes: a base fabric that has an LOI value of 25 or more, and that is a knitted body of a yarn including a flame-retardant fiber having an LOI value of 25 or more, a cellulose-based fiber, and a carbon fiber; an adhesion layer containing a flame retardant, the adhesion layer being provided at at least one side of the base fabric; and a skin layer provided at a side of the adhesion layer opposite to the side at which the base fabric is provided.

A base fabric of a synthetic leather refers to a base material for forming layers of the synthetic leather, the base material being a fabric selected from a knitted body, a woven fabric, a nonwoven fabric, or the like. The base fabric in the disclosure is a knitted body, that is, a knitted fabric formed by knitting with fibers.

[Base Fabric]

A base fabric used for the synthetic leather according to the disclosure is a knitted body of a yarn including a flame-retardant fiber having an LOI value of 25 or more (hereinafter, sometimes referred to as “flame-retardant fiber”), a cellulose-based fiber, and a carbon fiber, and has an LOI value of the base fabric itself, which is a knitted body, of 25 or more.

A knitted body used for the base fabric is knitted using including at least three different types of fibers described above.

A limiting oxygen index (LOI value) indicates an oxygen concentration required for a substance to continue burning, and is measured by the method described in JIS K7201 (2006) (ASTM D2863). Usually, since the oxygen concentration in the air is about 21.2%, it can be said that the flame retardancy is favorable when the LOI value is 25 or more.

Considering the case in which the base fabric is a base fabric for a synthetic leather used for interior materials of vehicles or the like, from the viewpoint of favorable knittability, and flexibility and durability of a base fabric to be obtained, it is preferable that a yarn used for knitting the knitted body has a thickness of about 16 count to 40 count. The term “count” herein means “cotton yarn count”, indicating that one pound of yarn (1 Lb: 0.45259237 kg) has a length of 840 yards (1 yard: 768.096 m). If one pound of yarn has a length of 1680 yards, it is called 2 count. Therefore, the smaller the count value is, the thicker the fiber is.

1 tex according to the SI unit system indicates that a 1000 m long yarn has a mass of 1 g. Cotton yarn count can be converted to tex using the following conversion formula.

1 tex=590.54 count (cotton yarn count)   (conversion formula)

(Flame-Retardant Fiber)

A flame-retardant fiber used for the base fabric is not particularly limited as long as the LOI value is 25 or more. A flame-retardant fiber refers, not to an incombustible fiber, but to a fiber in which burning does not spread even when, for example, a fiber or a knitted body of a fiber comes into contact with a flame thereby being charred or a portion at which the flame came into contact being burned, and in which the burning stops promptly when the flame is detached.

As a flame-retardant fiber, a flame-retardant synthetic fiber is preferable from the viewpoint of being able to form a soft and voluminous knitted body. Specific examples of the flame-retardant fiber that may be used for the base fabric include an aramid fiber including a meta-aramid fiber, a polyphenylene sulfide fiber, a polyclar fiber, a vinylidene chloride fiber, an acrylic-vinyl chloride copolymer fiber, an acrylic-vinylidene chloride copolymer fiber, a polybenzimidazole fiber, a vinylidene chloride fiber, and a vinyl chloride-based fiber. A fiber obtained by subjecting a non-flame retardant fiber to a flame-retardant processing to adjust the LOI value to 25 or more may be used as a flame-retardant fiber in the base fabric. Examples of a fiber which is obtained by the flame-retardant processing to adjust the LOI value to 25 or more include a flame retardant polynosic fiber, a flame-retardant polyester fiber, a flame-retardant acrylic fiber, and a flame-retardant rayon fiber.

From the viewpoint of simplicity of manufacturing and suppression of smoke generation, it is preferable to use a flame-retardant fiber in which the material itself of the fiber is flame retardant.

Among the flame-retardant fibers described above, it is preferable to include one or more selected from the group consisting of an aramid fiber, a meta-aramid fiber, a polyphenylene sulfide fiber, an acrylic fiber, a vinyl chloride fiber, a polyclar fiber, a vinylidene chloride fiber, an acrylic-vinyl chloride copolymer fiber, and an acrylic-vinylidene chloride copolymer fiber, from the viewpoint of flame retardancy and preferable strength and texture when knitted into a base fabric.

The flame-retardant fiber in the disclosure has an LOI value of 25 or more. The LOI value of the flame-retardant fiber is preferably 26 or more, and more preferably 28 or more.

Considering the case in which the base fabric for synthetic leather is used for interior materials of vehicles or the like, it is preferable that the thickness of a yarn including a flame-retardant fiber used for the knitting of a knitted body is from about 16 count to 40 count.

(Cellulose-Based Fiber)

A cellulose-based fiber used for the base fabric is not particularly limited, and any known cellulose-based fiber may be selected and used. Examples of the cellulose-based fiber include cotton, hemp, cupra, and rayon.

Among others, from the viewpoint of flexibility of a base fabric to be obtained, one or more selected from the group consisting of cotton and rayon is preferred.

A cellulose-based fiber such as cotton or rayon has an LOI value of about from 17 to 19 in itself, and can be said to be a flammable fiber. However, by combining a cellulose-based fiber with the above-described flame-retardant fiber and a carbon fiber described below to obtain a knitted body, the knitted body is used in an embodiment in which the LOI value of the whole base fabric, which is the knitted body, is 25 or more, while the characteristics of the cellulose-based fiber is well utilized.

By including a cellulose-based fiber in a yarn used for knitting the base fabric, the cellulose-based fiber is carbonized during burning, and the burning speed of a knitted body can be delayed.

(Carbon Fiber)

A carbon fiber refers to a fiber obtained by subjecting a carbon fiber precursor such as an organic fiber to heat carbonization treatment, the fiber having a mass ratio of 90% by mass or more of carbon to the total mass of the fiber.

There is no particular limitation on a carbon fiber used for producing a base fabric of the synthetic leather according to the disclosure.

In particular, the carbon fiber preferably includes at least one selected from the group consisting of a PAN (polyacrylonitrile)-based carbon fiber in which an acrylic fiber is used, a pitch-based carbon fiber in which a pitch is used as a raw material, and a phenolic carbon fiber in which a phenolic resin is used as a raw material. In other words, the base fabric is preferably knitted using a spun yarn including one or more selected from the group consisting of a polyacrylonitrile (PAN)-based fiber, a pitch-based fiber, and a phenolic fiber as a carbon fiber.

A carbon fiber mainly contains hydrogen and oxygen derived from a raw material resin as an element other than carbon. However, since a carbon fiber does not contain elements such as phosphorus, it is hard to burn, and there is very little smoke when burned. Furthermore, since a carbon fiber has high thermal conductivity, by the base fabric including a carbon fiber, spreading of fire at the time of ignition is effectively suppressed.

In the yarn including at least a flame-retardant fiber, a cellulose-based fiber, and a carbon fiber described above, which is used for knitting a base fabric, a manner in which each fiber is included is not particularly limited. For example, a base fabric may be knitted using three yarns, a yarn including a flame-retardant fiber, a yarn including a cellulose-based fiber, and a yarn including a carbon fiber. A base fabric may be knitted using a blended yarn including two of the three types of fibers and a yarn including the remaining one. A base fabric may be knitted using a blended yarn including the three types of fibers described above.

In order to obtain an excellent retarding effect on the burning speed by carbonization of the above-described cellulose fiber without impairing the flame retardancy of a base fabric, the cellulose-based fiber is preferably blended with the flame-retardant fiber and the carbon fiber described above.

In other words, from the viewpoint of the effect of retarding the burning speed and the effect of suppressing the generation of smoke, a yarn used to produce a knitted body is preferably a blended yarn selected from a blended yarn of a flame-retardant fiber and a cellulose-based fiber, a blended yarn of a carbon fiber and a cellulose-based fiber, or a blended yarn of a flame-retardant fiber, a cellulose-based fiber and a carbon fiber. Among those, a blended yarn of a flame-retardant fiber, a cellulose-based fiber, and a carbon fiber is preferable from the viewpoint that the flame retardancy and the smoke suppression effect is more favorable.

By using a yarn including the three types of fibers described above, a knitted body to be obtained can have an LOI value of 25 or more.

The contents of a flame-retardant fiber, a cellulose-based fiber, and a carbon fiber in a base fabric are appropriately adjusted such that the LOI value of a knitted body to be obtained can be 25 or more.

A base fabric used for the synthetic leather according to the disclosure is a knitted body knitted with a yarn including a flame-retardant fiber, a cellulose-based fiber, and a carbon fiber, the LOI value of the knitted body itself also being 25 or more.

It is preferable that the content of the carbon fiber with respect to the total mass of a yarn constituting the knitted body is from 20% by mass to 40% by mass, and the content of the cellulose-based fiber with respect to the total mass of a yarn constituting the knitted body is from 25% by mass to 45% by mass, and the total content of the flame-retardant fiber and the carbon fiber is greater than the content of the cellulose-based fiber.

In other words, from the viewpoint that the flame retardancy of the base fabric to be obtained becomes more favorable, the total content of the flame-retardant fiber and the carbon fiber in a knitted body is preferably more than 50% by mass, and the ratio of the total amount of the flame-retardant fiber and the carbon fiber with respect to the total mass of the yarn constituting the knitted body is from 60% by mass to 90% by mass.

The content of the carbon fiber with respect to the total mass of the yarn constituting a knitted body is preferably from 20% by mass to 40% by mass, and more preferably from 30% by mass to 40% by mass from the viewpoint of the smoke suppression effect.

From the viewpoint that the softness and texture of the base fabric to be obtained are more favorable, the content of the cellulose-based fiber is preferably from 25% by mass to 45% by mass, and more preferably from 25% by mass to 40% by mass with respect to the total mass of the yarn constituting the knitted body.

A knitted body preferably has an interlock knitted structure.

By making a knitted body, which is a base fabric, into an interlock knitted structure, texture and elasticity of the synthetic leather resulting from the base fabric become more favorable.

From the viewpoint of elasticity and strength of a base fabric to be obtained, preferably, the thickness of the yarn used for knitting a knitted body having an interlock knitted structure with a yarn including a flame-retardant fiber, a cellulose-based fiber, and a carbon fiber is about from 20 count to 40 count, and the yarn density is wale: about from 20 yarns/inch (=25.4 mm) to 50 yarns/inch, and course: about from 15 yarns/inch to 70 yarns/inch.

The mass of the thus obtained knitted body is preferably in the range of from 150 g/m² to 400 g/m², and more preferably in the range of from 175 g/m² to 350 g/m².

There is no particular limitation on the structure of the knitted body. The knitted body may be made uniform using a blended yarn obtained by twisting a flame-retardant fiber, a cellulose-based fiber, and a carbon fiber. The knitted body may be formed as an interlock knitted structure obtained by using a yarn made of a flame-retardant fiber, a yarn made of a cellulose-based fiber and a yarn made of a carbon fiber separately, in which the flame-retardant fiber and the carbon fiber are mainly exposed on one side and the cellulose fiber is mainly exposed on the other side.

In a case in which an interlock knitted structure is made using a yarn made of a flame-retardant fiber, a yarn made of a cellulose-based fiber, and a yarn made of a carbon fiber, flame retardancy of a specific side may be improved by knitting in such a manner as to expose a yarn including a flame-retardant fiber and a yarn including a carbon fiber on a side which requires better flame retardancy.

In particular, from the viewpoint that the texture, specifically the flexibility of a knitted body is more preferable, a yarn suitable for knitting a base fabric is a twisted yarn (blended yarn), and also from the viewpoint of improving the flame retardancy effect, a blended yarn including a flame-retardant fiber, a cellulose-based fiber, and a carbon fiber is preferable.

In other words, in a case in which an interlock knitted structure is formed using a blended yarn including a flame-retardant fiber, a cellulose-based fiber, and a carbon fiber, a favorable texture attributed to the cellulose-based fiber is obtained; during burning, besides being hard to burn, the cellulose-based fiber in the blended yarn is carbonized, whereby the burning speed of the knitted body is lowered; and, by the presence of a carbon fiber which has high thermal conductivity and by which the generation of smoke during burning is suppressed, the flame retardancy of a base fabric and the effect of suppressing smoke generation during burning become considerable.

As a preferable aspect of the interlock knitted structure, mockrody knitting, which is fine interlock knitting; ponterome knitting, which is one of modified structures of interlock knitting, and is a structure that alternately repeats interlock knitting and tacking plain stitch; and the like are preferable from the viewpoint of favorable strength and elasticity and excellent processability of a synthetic leather to be obtained.

For example, in the case of a knitted body having a mockrody knitted structure, since the structure is interlock knitted and has a high gauge, the structure is dense, has an appearance resembling a woven fabric, has a thick feeling, and has a flexibility and stretchability unique to a knitted body. In the case of a knitted body in which a base fabric is mockrody knitted, it is preferable to use a blended yarn of the above-described flame-retardant fiber, cellulose-based fiber, and carbon fiber. A gauge indicates the number of meshes per unit length, and a high gauge indicates a high density knitted body having a large number of meshes per unit length.

For example, in the case of a knitted body having a ponterome knitting, a knitted body can be formed in which a first yarn is mainly exposed on one side and a second yarn is mainly exposed on the other side. Therefore, by exposing a yarn made of a flame-retardant fiber and a carbon fiber on one side, making it a front side, and making the side on which the flammable cellulose-based fiber is exposed a back side, for example, a knitted body in which the cellulose-based fiber is protected by a layer made of the flame-retardant fiber and the carbon fiber can be obtained.

When adopting interlock knitting for knitting a base fabric, a blended yarn of the same composition may be used, or two types of blended yarn with different blending ratios may be used. In either case, by using the three types of fibers in combination, flame retardancy of the entire base fabric is improved, and generation of smoke during burning is effectively suppressed.

Since a knitted body of a yarn including a flame-retardant fiber, a cellulose-based fiber, which is natural fiber and has excellent breathability and texture, and a carbon fiber, which has high strength and flame resistance, high thermal conductivity, and which is hard to generate smoke even when heated, is used as a base fabric, a base fabric having excellent strength and texture, favorable flame retardancy, suppressed ability to generate smoke and high LOI value can be obtained. Since, in the synthetic leather according to the disclosure, an adhesion layer further contains a flame retardant as described later, it is considered that a combination of the flame retardancy of the base fabric and the flame retardancy of the adhesion layer provides a synthetic leather with favorable flame retardancy.

In the synthetic leather according to the disclosure, in addition to favorable flame retardancy of a base fabric and suppressed ability to generate smoke during burning, a synthetic leather formed using this base fabric is excellent in strength and processability, since the base fabric is excellent in strength and elasticity and is flexible.

The base fabric, which is a knitted body, may be napped on at least one side. Napping can be formed by a conventional method. Contacting a napped surface of the base fabric with an adhesion layer containing a flame retardant described later improves adhesion, adhesive strength and the like between the base fabric and the adhesion layer.

A base material used for the synthetic leather may be a single-layer base material having only a base fabric, or may be a base material having a multilayer structure in which base fabric and a sheet having physical properties according to a desired purpose are layered.

Hereinafter, respective layers of the synthetic leather according to the disclosure are described.

[Skin Layer]

Any known skin layer used for a synthetic leather may be used without limitation for the synthetic leather according to the disclosure.

In particular, the skin layer preferably contains a polyurethane from the viewpoint of excellent scratch resistance and processability.

As described in detail below, a skin layer may be formed by applying a composition for forming a skin layer containing a resin to the surface of a release agent layer of a temporary support including the release agent layer, and drying.

Examples of the polyurethane that may be used for a composition for forming a skin layer include a polycarbonate-based polyurethane, a polyether-based polyurethane, a polyester-based polyurethane, and a modified product thereof, and when long-term durability is desired, a polycarbonate-based polyurethane is preferred.

A polyurethane contained in the composition for forming a skin layer may be water-based or solvent-based.

A polyurethane used in the composition for forming a skin layer may be used alone, or two or more kinds thereof may be used in combination. When using two or more kinds of polyurethane, for example, a polycarbonate-based polyurethane, which is a preferable polyurethane, and a polyurethane other than the polycarbonate-based polyurethane may be used in combination.

Examples of the water-based polyurethane include an aquous polyurethane in which, using a polyether-based polyurethane (homopolymer), a polycarbonate-based polyurethane (homopolymer), or a mixture or copolymer of a polyether-based polyurethane and a polycarbonate-based polyurethane, from 0.01% to 10%, preferably from 0.05% to 5%, and more preferably from 0.1% to 2% by mass of carboxyl groups with respect to the polyurethane main agent is introduced into a part of a molecular chain of the polyurethane main agent described above. When a carboxyl group is introduced to the polyurethane main agent in the ranges of the mass ratio described above, due to the presence of the carboxyl group, the water-based polyurethane can have sufficient water dispersibility and dry film-forming properties.

Examples of the solvent-based polyurethane include at least one solvent-based polyurethane selected from the group consisting of a polycarbonate-based polyurethane, a polyether-based polyurethane, a polyester-based polyurethane, and a modified product thereof, which is soluble to an organic solvent. The solvent-based polyurethane may be a one-component system or a two-component system.

The skin layer preferably has a crosslinked structure from the viewpoint that the film strength of the skin layer is more favorable.

For example, in an embodiment in which a crosslinked structure is introduced into an water-based polyurethane, in a case in which a polyurethane main agent into which a carboxyl group has been introduced is used, for example, by adding a crosslinking agent to the composition for forming a skin layer, the carboxyl group and the crosslinking agent can be reacted to form a crosslinked structure.

Examples of the crosslinking agent which may be used for the composition for forming a skin layer in order to form a crosslinked structure include a conventionally known crosslinking agent. Examples thereof include an isocyanate crosslinking agent, an epoxy crosslinking agent, an aziridine crosslinking agent, a carbodiimide crosslinking agent, and an oxazoline-based crosslinking agent. In particular, it is preferable to use a carbodiimide crosslinking agent from the viewpoint of suppressing hydrolysis of the polyurethane.

Examples of an embodiment in which a crosslinked structure is introduced into a solvent-based polyurethane include an embodiment in which a solvent-based polyurethane is used as a main agent and in which polydiisocyanate is used in combination as a crosslinking component. By using a polydiisocyanate in combination, a crosslinked structure can be formed by heat curing of the polyurethane.

The polyurethane used to form a skin layer is preferably a polyurethane capable of forming a film having a hardness in the range of from 2 MPa to 40 MPa, and more preferably in the range of from 3 MPa to 10 MPa, at 100% modulus as measured according to JIS K6772 (1994).

The preferable hardness of the polyurethane used for the skin layer herein is a hardness after forming a crosslinked structure in the skin layer.

A commercially available product may be used as a polyurethane contained in the composition for forming a skin layer. Examples of the commercially available product that may be used for the composition for forming a skin layer include CRISVON (registered trademark) NY-373 (trade name) manufactured by DIC Corporation.

The skin layer may further contain other components in addition to the resin, which is a main component such as a polyurethane, and a solvent for dissolving the resin.

Examples of such other component that may be contained in the skin layer include the above-described crosslinking agent, a crosslinking accelerator, a colorant, a brightening agent (such as a pearlescent agent, or a metallic pigment), a light stabilizer, an ultraviolet absorber, an antioxidant, a feel improver, a film-forming aid, a flame retardant, and a blowing agent.

Examples of the colorant include colored organic resin particles in which a colorant is contained in organic resin fine particles selected from urethane-based resin particles, acrylic resin particles, or silicone-based resin particles. In particular, it is preferable to include polycarbonate-based colored resin particles, from the viewpoint of the affinity to the polyurethane-based resin, which serves as a dispersion medium, and uniform dispersibility.

In general, the average particle diameter of organic resin fine particles used as the colorant is preferably in the range of from 0.01 μm to 1.0 μm, and more preferably in the range of from 0.05 μm to 0.8 μm.

For example, when the skin layer contains a colorant, the designability of the synthetic leather is improved.

By adding a known flame retardant such as a phosphorus-based, halogen-based, or inorganic metal-based flame retardant to a skin layer, the flame retardancy of the synthetic leather is further improved.

The thickness of the skin layer is not particularly limited, and may be appropriately selected according to the purposes. In general, from the viewpoint of strength and appearance, the thickness of the skin layer after drying is preferably about from 10 μm to 50 μm, and more preferably about from 10 μm to 30 μm.

[Adhesion Layer Containing Flame Retardant]

The synthetic leather according to the disclosure has an adhesion layer containing a flame retardant (hereinafter, sometimes simply referred to as “adhesion layer”) provided at a side of the skin layer at which the base fabric is provided. In other words, the skin layer is located at a side of the adhesion layer opposite to the side at which the base fabric is provided.

An adhesion layer may be formed using a composition for forming an adhesion layer containing an adhesive and a flame retardant, as described below.

A polyurethane adhesive may be used to form an adhesion layer. Examples of the polyurethane which may be used for formation of an adhesion layer include a polycarbonate-based polyurethane, a polyether-based polyurethane, a polyester-based polyurethane, and a modified product thereof, and when long-term durability is desired, a polycarbonate-based polyurethane is preferred.

The polyurethane used for an adhesion layer may also be water-based or solvent-based, as with the polyurethane used for the skin layer.

The polyurethane used to form an adhesion layer is preferably a polyurethane capable of forming a film having a hardness in the range of from 2 MPa to 20 MPa, and more preferably in the range of from 2 MPa to 8 MPa, at 100% modulus as measured according to JIS K6772 (1994).

From the viewpoint of further improving the flexibility of the synthetic leather to be obtained, the polyurethane used for the adhesion layer is preferably a polyurethane which is equivalent to a polyurethane used for the skin layer or a polyurethane which is capable of forming a more flexible film.

A commercially available polyurethane may be used as a polyurethane contained in the composition for forming an adhesion layer. Examples of the commercially available product which may be used for the composition for forming an adhesion layer include CRISVON TA205FT manufactured by DIC Corporation.

(Flame Retardant)

An adhesion layer contains a flame retardant. The flame retardant contained in the adhesion layer can further improve the flame retardancy of the synthetic leather according to the disclosure. Therefore, the synthetic leather according to the disclosure is favorably used as interior materials for aircraft, vehicles, and the like.

The flame retardant which may be used for the adhesion layer is not particularly limited, and a known one can be appropriately used. Examples of the flame retardant include a metal hydroxide, a phosphorus-based flame retardant, and a nitrogen-phosphorus-based flame retardant.

The flame retardant is also available as a commercial product, and examples thereof include PEKOFLAM (registered trademark) STC powder manufactured by Archroma Japan K.K.

The content of the flame retardant is preferably in the range of from 5 parts by mass to 40 parts by mass with respect to 100 parts by mass of a polyurethane, which is a main component of the adhesion layer.

As will be described later, after a skin layer is formed on a temporary support, a composition for forming an adhesion layer including a polyurethane and a flame retardant is applied to the surface of the skin layer and dried by heating, whereby a layer of a coating liquid for forming an adhesion layer having a desired thickness is formed.

After that, thermocompression bonding is performed in such a manner that the base fabric described above and a layer of the composition for forming an adhesion layer are in contact with each other, and an adhesive contained in the layer of a composition for forming an adhesion layer is reacted and cured, whereby formation of an adhesion layer and adhering of the adhesion layer and the base fabric are performed simultaneously, and then, a temporary support is peeled off, and a synthetic leather can be obtained.

A crosslinking agent and a crosslinking accelerator may be added to the adhesion layer for the purpose of improving the curability.

The crosslinking agent and the crosslinking accelerator are selected according to the type of the polyurethane used in the adhesion layer. Examples of the crosslinking agent and the crosslinking accelerator that may be used for the composition for forming an adhesion layer include the same ones as those described in the composition for forming a skin layer described above.

The crosslinking agent may be used in combination with a crosslinking accelerator suitable for the crosslinking agent.

The content of the crosslinking agent in the composition for forming an adhesion layer may be appropriately selected in consideration of the strength, flexibility and the like required for the adhesion layer.

The thickness of the adhesion layer after drying is preferably about from 20 μm to 100 μm, and more preferably in the range of from 30 μm to 80 μm. When the thickness of the adhesion layer is in the above-described ranges, a synthetic leather having sufficient elasticity and strength is formed.

The synthetic leather according to the disclosure may include another layer in addition to the base fabric, the adhesion layer, and the skin layer, as long as an effect is not impaired. Examples of another layer include an intermediate layer and a surface treatment layer.

[Intermediate Layer]

Depending on the purposes, such as to further improve the strength of a skin layer or to improve the flexibility and cushioning properties of a synthetic leather, the synthetic leather according to the disclosure may include an intermediate layer between the skin layer and the adhesion layer described above.

There are no particular restrictions on the configuration of the intermediate layer. From the viewpoint of strength and flexibility, an intermediate layer containing a polyurethane is preferred.

The polyurethane used for the intermediate layer may be water-based or solvent-based, as with the polyurethane used for the skin layer.

The polyurethane used to form the intermediate layer is preferably a polyurethane capable of forming a film having a hardness in the range of from 2 MPa to 20 MPa, and more preferably in the range of from 3 MPa to 10 MPa, at 100% modulus as measured according to JIS K6772 (1994).

The intermediate layer may be a resin layer containing air bubbles, for example, a polyurethane resin intermediate layer containing air bubbles, for the purpose of improving cushioning properties and the like.

The polyurethane that may be used to form an intermediate layer may be a commercially available product. Examples of the commercially available polyurethane which may be used for formation of an intermediate layer include CRISVON TK1015T manufactured by DIC Corporation.

The thickness of the intermediate layer may be appropriately adjusted according to the purposes. In general, the thickness of the intermediate layer after drying is preferably from 30 μm to 350 μm, and more preferably from 50 μm to 250 μm.

The intermediate layer may further contain a component such as a film-forming aid, a pigment, a flame retardant, a filler, an antiaging agent, an ultraviolet light absorbent, and an aromatic agent.

In particular, when the synthetic leather according to the disclosure has an intermediate layer, the intermediate layer preferably contains a flame retardant. When both an adhesion layer and an intermediate layer contain a flame retardant, the flame retardancy of the synthetic leather is further improved.

[Layer Structure of Synthetic Leather]

Examples of the layer structure of the synthetic leather according to the disclosure will be described with reference to the drawings.

FIG. 1 is a schematic sectional view showing an embodiment of a synthetic leather 10 of the invention.

The synthetic leather 10 of an embodiment (sometimes referred to as first embodiment) shown in FIG. 1 includes: the above-described base fabric 12; an adhesion layer 14 containing a flame retardant provided at one side of the base fabric 12; and a skin layer 16 provided at a side of the adhesion layer 14 opposite to the side at which the adhesion layer 14 is in contact with the base fabric 12. Herein, the expression that the synthetic leather 10 includes a base fabric 12, an adhesion layer 14, and a skin layer 16 means that the adhesion layer 14 and the skin layer 16 exist in this order from the base fabric 12 side, and does not exclude the presence of another layer optionally provided.

The method of producing the synthetic leather according to the disclosure is not particularly limited, and a known production method may be applied as appropriate.

Hereinafter, a preferred method of producing a synthetic leather will be described by taking a synthetic leather having a layer structure shown in FIG. 1 as an example.

[Formation of Skin Layer]

A skin layer may be obtained by applying a composition for forming a skin layer containing a resin, preferably a polyurethane to the surface of a release agent layer of a temporary support including the release agent layer with, for example, a closed or open coating head, forming a layer of a composition for forming a skin layer, and drying the layer of a composition for forming a skin layer by heating.

The skin layer can be formed to have a desired thickness by adjusting the formulation of the composition for forming a skin layer, the amount of application, and the like.

Examples of the temporary support used for forming a skin layer include a temporary support including a release agent layer on the surface, and including a desired embossed type (concave and convex pattern) formed on the surface on which the skin layer is to be formed.

For example, when producing a synthetic leather provided with a skin layer having a natural leather-like appearance, a leather-like concavo-convex pattern may be preformed on the surface of a temporary support on which a release agent layer is to be formed. By using a temporary support having a concavo-convex pattern formed on the surface as a temporary support, and applying a composition for forming a skin layer to the surface of the temporary support on which a release agent layer has been formed, the leather-like concavo-convex pattern preformed on the temporary support is transferred to the formed skin layer, and after peeling off the temporary support, the skin layer having the concavo-convex pattern is formed in a direction.

A method of forming a concavo-convex pattern on a skin layer is not limited to the above, and for example, it is also possible to form a concavo-convex pattern by conducting embossing when thermocompression of a plurality of layers including a skin layer is carried out.

A polyurethane that may be used for the composition for forming a skin layer is as described above.

The application amount and the film thickness of a skin layer are not particularly limited, and appropriately selected depending on the purposes. In general, from the viewpoint of strength and appearance, the thickness of the skin layer after drying is preferably about from 10 μm to 50 μm, and more preferably about from 10 μm to 30 μm.

[Formation of Adhesion Layer Containing Flame Retardant]

An adhesion layer is provided at a surface of the formed skin layer. The adhesion layer is provided at a surface of the skin layer opposite to the surface on which a concavo-convex pattern is formed.

After the skin layer is formed on the temporary support, a composition for forming an adhesion layer containing a polyurethane and a flame retardant is applied to the surface of the skin layer with a closed or open coating head to form a layer of a composition for forming an adhesion layer, which is dried by heating to form a layer of a coating liquid for forming an adhesion layer having a desired thickness.

After that, the above-described base fabric and the layered body including the skin layer and the layer for a composition for forming an adhesion layer formed on the temporary support are layered such that the side to which the layer of a composition for forming an adhesion layer is applied to comes into contact with the base fabric, and are thermocompression bonded, whereby the adhesive contained in the layer of a composition for forming an adhesion layer is reacted and cured, performing formation of an adhesion layer and adhering of the adhesion layer and the base fabric simultaneously. Thereafter, the temporary support is peeled off, whereby a synthetic leather is obtained.

The heating temperature and heating time for accelerating the curing reaction at the time of curing the layer of a composition for forming an adhesion layer to form an adhesion layer are appropriately selected depending on the type of an adhesive contained in the composition for forming an adhesion layer. In general, the heating temperature is preferably in the range of from 30° C. to 80° C., and the heating time is preferably in the range of from 12 hours to 72 hours.

When thermocompression bonding is performed, lamination is preferably performed at a heating temperature in the range of from 100° C. to 150° C. with a known device such as a roll nip device.

In a case in which the base fabric is napped on at least one side, by tightly adhering the napped side to the layer of a coating liquid for forming an adhesion layer, the nap of the base fabric infiltrates the layer of a coating liquid for forming an adhesion layer. Since the adhesion layer is cured in this state, adhesion between the base fabric and the adhesion layer is further improved.

As described above, in an example of a preferred method of producing a synthetic leather, by forming a layered body of a skin layer and a layer of a composition for forming an adhesion layer on a temporary support, tightly adhering and fixing the adhesion layer and a base fabric by curing the layer of a composition for forming an adhesion layer, and then peeling off the temporary support including a release layer, a synthetic leather having favorable elasticity, strength and flame retardancy with a suppressed ability to generate smoke during burning, such as a synthetic leather having the layer structure illustrated in FIG. 1, can be obtained.

FIG. 2 is a schematic sectional view showing a synthetic leather (sometimes referred to as “second embodiment”) 20 in another embodiment of the invention.

In the synthetic leather 20 according to the second embodiment, an intermediate layer 18 is provided between the adhesion layer 14 and the skin layer 16. By optionally providing the intermediate layer 18 between the adhesion layer 14 and the skin layer 16 according to the manner in which the synthetic leather is used, elasticity, flexibility, shape followability, and the like of the synthetic leather 20 becomes more favorable.

[Formation of Intermediate Layer]

There are no particular restrictions on the structure of the intermediate layer. From the viewpoint of strength and flexibility, an intermediate layer containing a polyurethane is preferred.

An intermediate layer may be obtained by, after the skin layer is formed on the temporary support as described above, applying a composition for forming an intermediate layer, preferably including a polyurethane, to the side of the skin layer opposite to the side at which the temporary support is located, to form a layer of a composition for forming an intermediate layer, drying the layer of a composition for forming an intermediate layer by heating, whereby a layered body having a skin layer and an intermediate layer on the temporary support can be formed. The application and drying of the composition for forming an intermediate layer may be repeated twice or more to form an intermediate layer having a desired thickness.

The intermediate layer may be a polyurethane intermediate layer containing air bubbles for the purpose of improving cushioning properties and the like. An example of a method of forming a polyurethane intermediate layer containing air bubbles will be described.

For example, by using a solvent and a thickener as appropriate for the composition for forming an intermediate layer containing a polyurethane to adjust the viscosity, and mechanically generating foams by stirring, a creamy composition for forming an intermediate layer containing air bubbles can be prepared. By applying the obtained creamy composition for forming an intermediate layer to the skin layer described above to form a layer of a composition for forming an intermediate layer containing air bubbles, and drying and curing the formed layer, a polyurethane intermediate layer containing air bubbles can be formed.

The composition for forming an intermediate layer to be mechanically foamed may contain a foaming agent, a foam stabilizer, a crosslinking agent, a thickener, and the like.

By using a commonly used batch stirrer such as a Hobart mixer or a hopper, the composition for forming an intermediate layer can be mechanically stirred while involving air, thereby obtaining a mechanically-foamed creamy composition for forming an intermediate layer. In mass production, it is possible to adopt a method of obtaining a mechanically-foamed creamy composition for forming an intermediate layer by continuously stirring while feeding a certain amount of air using an oakes mixer, a pin mixer, or the like.

When applying the mechanically-foamed creamy composition for forming an intermediate layer to the skin layer, a known coating apparatus such as a knife coater, a comma coater, a roll coater, a lip coater which is generally used can be employed.

Examples of another method of forming a polyurethane intermediate layer which contains air bubbles include a method in which a chemical blowing agent, such as a thermal expansion microcapsule, 4,4″-oxybis (benzenesulfonyl hydrazide), azodicarbonamide, or sodium hydrogen carbonate, is included in the composition for forming an intermediate layer, which is applied to the above-described skin layer, and then heat-dried so that the chemical blowing agent generates air bubbles, thereby forming an intermediate layer containing bubbles.

A synthetic leather having a layer structure illustrated in FIG. 2 can be obtained by applying, in the same manner as in the first embodiment described above, a composition for forming an adhesion layer to a side of the formed intermediate layer opposite to the side at which the skin layer is provided to form a layer of a composition for forming an adhesion layer, tightly adhering a base fabric and a face of the formed layer of a composition for forming an adhesion layer, curing the layer of a composition for forming an adhesion layer, and then peeling off the temporary support.

In a case in which a chemical blowing agent is used, the composition for forming an intermediate layer may contain, in addition to the chemical blowing agent, a foaming agent, a foam stabilizer, a crosslinking agent, a thickener, or the like.

The composition for forming an intermediate layer may further contain a component such as a film-forming aid, a pigment, a flame retardant, a filler, an antiaging agent, an ultraviolet light absorbent, and an aromatic agent.

[Formation of Other Layer]

The synthetic leather according to the disclosure may be provided with another layer in addition to the above-described skin layer, adhesion layer, and optionally provided intermediate layer provided at at least one side of the base fabric, as long as an effect of the disclosure is not impaired.

Formation of a surface treatment layer, which is an example of another layer, will be described below.

(Surface Treatment Layer)

A surface treatment layer can be formed by applying a surface treatment agent composition containing an water-based emulsion resin or an organic solvent-based surface treatment agent composition to the surface of the skin layer described above.

The resin used to form the surface treatment layer is not particularly limited, and any resin may be used depending on the purposes. As an example of the resin used for forming a surface treatment layer, a polyurethane, an acryl, an elastomer, or the like is preferable, and a polyurethane is more preferable.

By forming a surface treatment agent layer at the surface of a skin layer, the appearance of the synthetic leather is further improved.

The surface treatment layer may contain a crosslinking agent, an organic filler, a lubricant, a flame retardant, or the like. For example, by including an organic filler, a lubricant, or the like in the surface treatment layer, a smooth feel is imparted to the skin material, and abrasion resistance is further improved.

The synthetic leather according to the disclosure is excellent in durability and flame retardancy since the synthetic leather is provided with a base fabric with a suppressed ability to generate smoke during burning and an adhesion layer containing a flame retardant. Therefore, the synthetic leather can be used suitably for various fields such as automotive interior materials, railway vehicle interior parts, aircraft interior parts, furniture, shoes, footwear, bags, interior and exterior members for construction, clothing coverings, and clothing lining. Further, the synthetic leather exhibits an effect of, in the case of covering the surface of a member having a complex three-dimensional shape such as a seat or a chair, achieving similar feel and appearance as in the case of using a natural leather.

EXAMPLES

Hereinafter, the embodiments described above will be more specifically described by way of Examples. However, the invention is not limited to the following Examples, and various modifications can be made as long as they do not depart from the spirit of the invention.

Example 1

Using a blended yarn of 22 count in thickness obtained by spinning three kinds of fibers, which are: polyvinylidene chloride-acrylic copolymer fiber (LOI value: 33), which is a flame retardant; a rayon fiber (LOI value: 19), which is a cellulose-based fiber; and a phenolic carbon fiber, which is carbon fiber (LOI value: 33), a knitted body (knitted fabric), having a knitting structure of mockrody, a thickness of 0.9 mm, and a weight of 310 g/m², was manufactured, whereby a base fabric was obtained. The blending ratio of the polyvinylidene chloride fiber, the rayon fiber, and the phenolic carbon fiber was 35:35:30 by mass ratio.

The LOI value of the obtained base fabric measured in accordance with JIS K7201 (2006) was 37.

As a temporary support, a patterned release paper which has been release-treated on the surface and has a release layer (manufactured by Dai Nippon Printing Co., Ltd., DE-41: average paper thickness of 140 μm) was used.

(Composition for Forming Skin Layer)

Non-yellowing polycarbonate-based urethane resin with 100% modulus of 5 MPa (manufactured by DIC Corporation, CRISVON NY327: trade name): 100 parts by mass

Colored organic resin fine particles (DIC Corporation, Dirac (registered trademark) color series): 18 parts by mass

Solvent (mixed solvent of N,N-dimethylformamide (DMF) and isopropanol (IPA) in a mass ratio of 80:20): 36 parts by mass

The above composition for forming a skin layer was sufficiently mixed, and a composition for forming a skin layer was obtained.

The composition for forming a skin layer was applied to the surface of the temporary support having a release layer, at the side of the release layer in an amount by which the film thickness after drying became about 30 μm using an open coating head coating apparatus. The coating film was dried with hot air using a hot air drier at 100° C. for 2 minutes to form a skin layer on the temporary support. By visually observing the obtained skin layer, it was confirmed that the skin layer was uniform without pinholes.

(Composition for Forming Adhesion Layer)

Non-yellowing polycarbonate-based polyurethane adhesive with 100% modulus of 2.5 MPa (manufactured by DIC Corporation, CRISVON TA205FT: trade name): 100 parts by mass

Non-Deca BDE-based halogen-based flame retardant (combination with antimony) (manufactured by Marubishi Oil Chemical Corporation, NONNEN (registered trademark) SAN-2: trade name): 20 parts by mass

Solvent (mixed solvent of DMF and methyl ethyl ketone (MEK) with a mass ratio of 85:15): 65 parts by mass

Crosslinking agent (manufactured by DIC Corporation, BURNOCK (registered trademark) DN950: trade name): 10 parts by mass

The components of the composition for forming an adhesion layer were sufficiently mixed, and a composition for forming an adhesion layer was obtained.

On the surface of the temporarily formed skin layer at the side opposite to the side at which the temporary support was placed, the composition for forming an adhesion layer was applied in an amount by which the film thickness after drying became 50 μm using an open coating head, and was dried at 100° C. for 2 minutes to form a layer of a coating liquid for forming an adhesion layer, whereby a layered body for forming a synthetic leather was obtained.

Next, a base fabric and the layer of a coating liquid for forming an adhesion layer of the layered body for forming a synthetic leather were brought into contact with each other, which were then laminated by a nip device, were wound up, and were maintained at a temperature of 50° C. for 48 hours to allow the curing reaction of the adhesive contained in the layer of a coating liquid for forming an adhesion layer to proceed, whereby an adhesion layer tightly adhered to the base fabric was formed.

After that, the temporary support was peeled off, and a synthetic leather of Example 1, including an adhesion layer and a skin layer in this order at the surface of the base fabric, was obtained.

The obtained synthetic leather of Example 1 was visually observed. As a result, it was confirmed that there was no pattern loss due to emboss transfer failure, that the appearance was excellent, and that the elasticity and feel upon pressing the synthetic leather with a finger were favorable.

Example 2

A skin layer was temporarily formed on a release paper in the same manner as in Example 1.

Next, components of the following formulation were sufficiently mixed, and a composition for forming an intermediate layer was prepared.

(Composition for Forming Intermediate Layer)

Non-yellowing polycarbonate-based urethane resin with 100% modulus of 5 MPa (manufactured by DIC Corporation, CRISVON TK1015T): 100 parts by mass

Thermally expandable beads (Japan Fillite Co., Ltd., EXPANCEL 920DU120): 4 parts by mass

Amine chain extender (BASF Japan Ltd., LAROMIN (registered trademark) C260): 4.6 parts by mass

Colored organic resin fine particles (manufactured by DIC Corporation, DAILAK COLOR SERIES): 5 parts by mass

Phosphorus-based flame retardant (manufactured by Archroma Japan K.K., PEKOFLAM (registered trademark) ATC powder): 30 parts by mass

Solvent (mixed solvent of DMF, 1-methoxy-2-propanol (PGM), and ethyl acetate with a mass ratio of 24:38:38): 52 parts by mass

On the surface of the temporarily formed skin layer described above at the side opposite to the side at which the temporary support was placed, the obtained composition for forming an intermediate layer was applied in an amount by which the film thickness after drying became 200 μm using an open coating coater. The coated film was dried with hot air at 170° C. for 2 minutes using a hot air dryer, by which thermally expandable beads were expanded, whereby an intermediate layer containing air bubbles was formed on the skin layer.

A layer of a coating liquid for forming an adhesion layer was formed on the surface of the formed intermediate layer opposite to the side at which the skin layer is provided in the same manner as in Example 1, whereby a layered body for forming a synthetic leather was obtained.

Next, a base fabric, which is the same base fabric as used in Example 1, and the layer of a coating liquid for forming an adhesion layer of the obtained layered body for forming a synthetic leather were brought into contact with each other, and after drying of the layer of a coating liquid for forming an adhesion layer, the layered body was tightly adhered to the base fabric by thermocompression. In this manner, a synthetic leather of Example 2, which further includes an intermediate layer containing air bubbles in the synthetic leather of Example 1, was obtained.

The obtained synthetic leather of Example 2 was excellent in appearance, and the elasticity and feel upon pressing the synthetic leather with a finger were even more favorable than those of the synthetic leather of Example 1.

Comparative Example 1

A synthetic leather of Comparative Example 1 was produced in the same manner as in Example 1 except that a base fabric obtained by knitting in the same manner as in the base fabric in Example 1, using a 22 count blended yarn obtained by spinning two types of fibers, which are: polyvinylidene chloride-acrylic copolymer fiber (LOI value: 33), which is a flame retardant; and a rayon fiber (LOI value: 19), which is a cellulose-based fiber, at a mass ratio of 65:35, was used instead of the base fabric used in Example 1.

Comparative Example 2

A synthetic leather of Comparative Example 2 was produced in the same manner as in Example 1 except that a base fabric obtained by knitting in the same manner as in the base fabric in Example 1, using a 22 count yarn consisting only of a polyvinylidene chloride-acrylic copolymer fiber (LOI value: 33), which is a flame retardant, was used instead of the base fabric used in Example 1.

(Evaluation of Obtained Synthetic Leather)

The obtained synthetic leather was evaluated by the following method. The results are shown in Table 1 below.

1. Flame Retardancy Evaluation

The respective synthetic leathers obtained were subjected to a burning test according to the Airworthiness Standards, Part III, Appendix F, Vertical Method, and flame retardancy was evaluated according to the criteria 1-1 to 1-3 shown below.

Using criteria 1-1 to 1-3 below, flame retardancy was evaluated as A if all the categories fell within rank A, and the flame retardancy was evaluated as B if two of the categories fell within rank A and no category fell within the rejection level. When the flame retardancy shown in Table 1 was evaluated as A or B, it is concluded that the flame retardancy sufficient for practical use is exhibited.

1-1. Burning Time

The time for which burning lasted after ignition was measured. According to the Standards, cases in which burning stops within 15 seconds are considered to be acceptable.

-   A: Burning time is 5 seconds or less. -   B: Burning time is from more than 5 seconds to 10 seconds. -   C: Burning time is from more than 10 seconds to 15 seconds. -   D: Burning time is more than 15 seconds (rejection level).

1-2. Burning Length

The length of burning spreading from the ignition site was measured. According to the Standards, 20 cm or less is considered to be acceptable.

-   A: Burning length is 15 cm or less. -   B: Burning length is more than 15 cm to 20 cm. -   C: Burning length is more than 20 cm (rejection level).

1-3. Burning Time of Falling Objects

The time for which the burning of falling objects from the ignited point lasted was measured. According to the Standards, it is considered to be acceptable if the burning stops within 5 seconds.

-   A: Falling objects do not burn, and burning stops immediately. -   B: Burning time of falling objects is 5 seconds or less. -   C: Burning time of falling objects is more than 5 seconds (rejection     level).

2. Test for Smoke Generation Property

A test for smoke generation property of the synthetic leathers was performed by the measurement according to BSS 7238, Flame Method (measurement of the smoke specific optical density of aircraft interior materials, standards of Boeing Company) using a smoke chamber, and evaluation was performed according to the following criteria. If the smoke concentration was 100 or less, the smoke generation property was evaluated as acceptable for practical use.

(Evaluation Criteria)

-   A: Smoke concentration is 80 or less. -   B: Smoke concentration is more than 80 to 100. -   C: Smoke concentration is more than 100.

3. Anti-Fire Spreading Property

When a base fabric of a synthetic leather is melted and a hole is formed in the base fabric upon burning, burning of a polyurethane or the like used for an adhesion layer, an intermediate layer or the like of the synthetic leather is promoted. Therefore, a burning test was conducted from the skin layer side of the synthetic leathers, and evaluation as to whether or not a hole was formed in the base fabric upon burning was performed.

(Evaluation Criteria)

-   A: The burning point of a base fabric is carbonized, and a hole is     not formed. -   B: The burning point of a base fabric is melted, and a hole is     formed (rejection level).

4. Scratch Resistance

The scratch resistance at the side of the skin layer of the synthetic leathers was tested using Taber type Scratch Tester (manufactured by TESTER SANGYO Co., Ltd., HA-201) in accordance with the method described in JIS K6253 (2006), and evaluation was performed according to the following criteria. The required performance for scratch resistance is 2.94 N or more.

(Evaluation Criteria)

-   A: 2.94 N or more -   B: less than 2.94 N

TABLE 1 Base fabric for synthetic leather Evaluation results Flame-retardant Cellulose- Thickness of Smoke Anti-fire fiber based fiber Carbon fiber yarn for Base fabric Flame generation spreading Scratch (LOI value) (LOI value) (LOI value) base fabric (LOI value) retardancy property property resistance Example 1 Polyvinylidene Rayon fiber Phenolic carbon 22 count (blended 37 A A A A chloride-acrylic (19) fiber (33) yarn of 3 types of copolymer fiber (33) fibers) Example 2 Polyvinylidene Rayon fiber Phenolic carbon 22 count (blended 37 A A A A chloride-acrylic (19) fiber (33) yarn of 3 types of copolymer fiber (33) fibers) Comparative Polyvinylidene Rayon fiber — 22 count (blended 35 A B A A Example 1 chloride-acrylic (19) yarn of 2 types of copolymer fiber (33) fibers) Comparative 22 count — — 22 count (blended 33 A C B A Example 2 Polyvinylidene yarn of 1 type of chloride-acrylic fiber) copolymer fiber (33)

From the results shown in Table 1, it is understood that the synthetic leathers of Example 1 and Example 2 are excellent in all of the flame retardancy, the anti-fire spreading property, and the scratch resistance, and have a suppressed ability to generate smoke upon burning, whereby visibility during burning is expected to be secured. Therefore, it can be understood that the synthetic leathers can be suitably used for aircraft seat materials, vehicle interior materials, furniture, and the like, which are required to have flame retardancy and durability.

On the other hand, the synthetic leather of Comparative Example 1 using a flame-retardant fiber and a cellulose-based fiber as the base fabric was slightly inferior to Examples in suppressing the generation of smoke upon burning, and Comparative Example 2 using only a flame-retardant fiber had inferior anti-fire spreading property compared to Example 1, and the smoke generation property was also at a level that would cause problems in practical use.

The disclosure of Japanese Patent Application No. 2016-251706 filed on Dec. 26, 2016 is hereby incorporated by reference.

All Documents, Patent Applications, and technical standards described herein are incorporated by reference herein to the same extent as if each of the Documents, Patent Applications, and technical standards had been specifically and individually indicated to be incorporated by reference. 

1. A synthetic leather comprising: a base fabric that has a limiting oxygen index of 25 or more, and that is a knitted body of at least one yarn, each yarn comprising at least one of a flame-retardant fiber having a limiting oxygen index of 25 or more, a cellulose-based fiber, or a carbon fiber, and the base fabric includes the flame retardant fiber, the cellulose-based fiber, and the carbon fiber; an adhesion layer containing a flame retardant, the adhesion layer being provided at at least one side of the base fabric; and a skin layer provided at a side of the adhesion layer opposite from a side at which the base fabric is provided.
 2. The synthetic leather according to claim 1, wherein the flame-retardant fiber comprises one or more selected from the group consisting of an aramid fiber, a meta-aramid fiber, a polyphenylene sulfide fiber, an acrylic fiber, a vinyl chloride fiber, a polyclar fiber, a vinylidene chloride fiber, an acrylic-vinyl chloride copolymer fiber, an acrylic-vinylidene chloride copolymer fiber, and an a polybenzimidazole fiber.
 3. The synthetic leather according to claim 1, wherein the carbon fiber comprises one or more selected from the group consisting of a polyacrylonitrile-based fiber, a pitch-based fiber, and a phenolic fiber.
 4. The synthetic leather according to claim 1, wherein: a content of the carbon fiber is from 20% by mass to 40% by mass with respect to a total mass of the yarn constituting the knitted body, a content of the cellulose-based fiber is from 25% by mass to 45% by mass with respect to the total mass of the yarn constituting the knitted body, and a total content of the flame-retardant fiber and the carbon fiber is greater than the content of the cellulose-based fiber.
 5. The synthetic leather according to claim 1, further including an intermediate layer between the adhesion layer and the skin layer.
 6. The synthetic leather according to claim 5, wherein the intermediate layer comprises a flame retardant. 